Known friction clutches provide a releasable torsional connection between a motor vehicle engine flywheel and an associated transmission. Repeated clutch disengagement and engagement cycles wear the friction material of the clutch driven disc. The wear results in an axial shift of the pressure plate's position toward the flywheel in the engaged condition. The axial shift commonly decreases the clutch engagement force or clamping load.
Some clutches are commonly provided with an adjustment mechanism which automatically compensates for driven disc wear and maintains the clutch engagement force. Some automatic adjustment mechanisms are disposed between the pressure plate and an associated biasing member such as a diaphragm spring. The biasing member acts against the adjustment mechanism to bias the pressure plate toward the flywheel. The clutch engagement force developed by the biasing member prevents adjustment of the adjustment mechanism in the engaged condition. When the clutch is released, the clutch engagement force is eliminated, enabling automatic adjustment of the clutch. However, over adjustment can occur.
It is known to provide adjustment limiters in the form of finger elements connected to the pressure plate. The fingers limit the travel of the adjusting feature relative to the pressure plate. As the driven disc wears, the fingers are forced further out, allowing the adjustment mechanism to further adjust. However, the finger elements have several disadvantages. One disadvantage is that the effectiveness of the fingers depends on the dimensions of the fingers, the dimensions of the pressure plate, and the dimensions adjustment mechanism components. The interdependence of these parts makes it difficult to provide assemblies with optimally compatible component dimensions.
Another disadvantage of finger systems is that the fingers may not properly compensate for wear of the driven disc. The fingers engage the adjustment mechanism at a location radially offset from where the adjustment mechanism is engaged by the spring. Any axial deflection or wear of the adjustment mechanism which changes the axial distance between the spring and finger engagement locations will resultantly either decrease the pressure plate departure distance or decrease the clutch engagement force.
Another disadvantage of the finger system is that the flywheel surface engaged by the ends of the fingers which pass through the pressure plate must be a flat, controlled surface. Otherwise, the fingers will not be displaced equally, and may allow the adjusting mechanisms to cock, or may result in an incorrect adjustment.
Yet another disadvantage of a finger system is that the fingers are in the immediate vicinity of the frictional engagement surface of the pressure plate where a significant amount of heat is generated during clutch engagements. This heat may affect the operation of the fingers.
It is desired to provide a clutch having an adjustment mechanism with a travel limiter relatively insensitive to dimensional variations of the pressure plate and the adjustment mechanism.
It is desired to provide a clutch having an adjustment mechanism with a travel limiter which is relatively insensitive to deflection or wear.
It is desired to provide a clutch having an adjustment mechanism with a travel limiter which is relatively insensitive to variations of the flywheel surface characteristics.
It is desired to provide a clutch having an adjustment mechanism with a travel limiter which is relatively insensitive to temperature increase of the pressure plate.